1. Field of the Invention
The present invention relates to a message bit terminating system in an SLC96 interface used between remote stations and a switching center according to U.S. standards.
2. Description of the Related Art
In the US, the ratio of direct convention of subscribers' line to a switching center (CO station: central office) is low. Since houses are dispersed in a wide area, a large number of subscriber lines are connected at a remote station (RT station), and an interface for connecting these remote stations to the switching center is stipulated as a standard. This standard is referred to as LSSGR (LATA Switching System Generic Requirement where LATA is an abbreviation for Local ACCESS TRANSPORT Area).
The LSSGR standard stipulates a communication interface, using time division multiplexing, called the SLC96 Interface, as an interface between the RT stations and the CO station. According to the SLC96 interface standard, messages such as connection control information, alarm information, switching control information for fault conditions, and so forth, are exchanged between the CO station and the RT stations together with speech signals. Therefore, efficient processing of this message information is desired.
The connection network type to which the conventional LSSGR standard is applied in the US is the type where a plurality of remote stations (RT) are connected to the switching center (CO). The switching center is able to effect the exchange of messages by using a time-division multiplexing digital switch. The remote station accommodates 96 subscriber terminals or 48 subscriber terminals, for example, and the SLC96 standard is stipulated for the interface at the switching center so as to effect time-division multiplex transmission of digital signals. A subscriber line to each remote station can be connected to and communicate with a subscriber line directly connected in the switching center or a subscriber line at other remote station or a subscriber line at an other switching center through the switching center.
When the subscriber connection procedure information is processed in a 9 ms cycle by the software in the SLC96 interface, as described above, there exists the problem that the load on the processor increases when the number of the SLC96 interfaces accommodated in the switching center increases.
When the message processing described above is executed by the data terminal DT (or by the DT controller DTC) at the switching center, a microprocessor becomes necessary and, in this case too the number of microprocessors increases when the number of the SLC96 interfaces connected to the system increases, so that the system cost increases.